1. Field of the Invention
The present invention relates to an elastic wave device using elastic waves such as surface acoustic waves or boundary acoustic waves, and more specifically to an elastic wave device having a structure in which an elastic wave filter chip is mounted on a die-attach surface of a wiring board.
2. Description of the Related Art
In recent years, a branching filter has been connected to an antenna of a cellular phone or the like to isolate signals transmitted and received by the antenna. As the branching filter, an elastic wave branching filter using elastic waves such as surface acoustic waves, boundary acoustic waves, or bulk acoustic waves has been widely used.
For example, Japanese Unexamined Patent Application Publication No. 2003-249842 discloses an example of this type of branching filter using elastic waves.
As illustrated in FIG. 13, a branching filter 1001 described in Japanese Unexamined Patent Application Publication No. 2003-249842 includes a common terminal 1002 connected to an antenna, a transmission terminal 1003, and a reception terminal 1004. A transmission surface acoustic wave filter 1005 is connected between the common terminal 1002 and the transmission terminal 1003. The transmission surface acoustic wave filter 1005 is a ladder surface acoustic wave filter in which the illustrated electrode structure is formed on a piezoelectric substrate.
A reception filter 1006 is connected between the common terminal 1002 and the reception terminal 1004. The reception filter 1006 includes longitudinally coupled resonator-type dual-mode surface acoustic wave filters 1007 and 1008. That is, the longitudinally coupled resonator-type dual-mode surface acoustic wave filters 1007 and 1008 are formed on a piezoelectric substrate. The longitudinally coupled resonator-type dual-mode surface acoustic wave filters 1007 and 1008 are connected to an input signal terminal 1009 by a common connection wiring line 1010. The input signal terminal 1009 is connected to the common terminal 1002 via a matching circuit 1011. Respective output terminals of the longitudinally coupled resonator-type dual-mode surface acoustic wave filters 1007 and 1008 are commonly connected to a signal terminal 1012. That is, the output terminals of the longitudinally coupled resonator-type dual-mode surface acoustic wave filters 1007 and 1008 are commonly connected to the signal terminal 1012 by a common connection wiring line 1013. The signal terminal 1012 is connected to the reception terminal 1004.
In the branching filter 1001 described in Japanese Unexamined Patent Application Publication No. 2003-249842, the reception filter 1006 has the two longitudinally coupled resonator-type dual-mode surface acoustic wave filters 1007 and 1008 connected in parallel between the input and output signal terminals. It is therefore possible to halve the aperture length of the surface acoustic wave filter, as compared with a structure in which a single longitudinally coupled resonator-type dual-mode surface acoustic wave filter is connected between the input and output terminals. Accordingly, it is possible to reduce the resistance value of electrode fingers to one quarter thereof, and thus to reduce the insertion loss. It is also possible to improve the electric power handling capability.
However, since the plurality of longitudinally coupled resonator-type dual-mode surface acoustic wave filters 1007 and 1008 are connected in parallel, as described in Japanese Unexamined Patent Application Publication No. 2003-249842, the input signal terminals and the output signal terminals are required to be commonly connected. It is therefore necessary to form the above-described common connection wiring lines 1010 and 1013 on the piezoelectric substrate of the reception filter 1006. Accordingly, the reception filter 1006 thus is undesirably increased in chip size.